Consumer Reports: Secrets for getting the cheapest airfare

If you're planning a flight for the December holidays and haven't booked yet, do it soon. Consumer Reports says if you wait much longer, you'll probably see prices jump.

Here's how to find the cheapest price:

For many air travelers, getting the lowest price is what matters the most. But which booking site will give you the best deal?

Consumer Reports compared nine sites, searching for the cheapest nonstop round-trip flights for five busy domestic routes. Users simultaneously searched for the exact same itinerary at the same time to the same airport.

They found there could be big differences. For example, in a search for New York to Miami round-trip flights, the cheapest fare Google Flights came up with was $597. But on Priceline, the cheapest was $459. And despite its name, CheapOAir never came up with the lowest fare on any of the routes that Consumer Reports checked.

You'll increase your odds of finding the lowest fare if you search for flights multiple times over multiple days with and without your search history cleared on your browser.

Also check the airlines own sites to see if you can find an even lower fare. You can find all airlines that serve a given route at google.com/flights.

Fares can vary considerably for flights just hours apart and at nearby airports.

Consumer Reports found that Kayak makes it particularly easy to search for other options.

With prices changing all of the time, Consumer Reports says it's a good idea to check the day after you book to see whether you can find a better deal. By law you can cancel without penalty for 24 hours after you book it, as long as you're not traveling for at least a week.